1. Field of the Invention
This invention relates to voltage converters and more particularly to start-up of voltage converters.
2. Description of the Related Art
Voltage converters are used in various applications to translate an input voltage to an output voltage. Switching converters may provide, e.g., regulated DC output voltage from an unregulated AC input or a translated DC output from a DC input. Such converters can be required when the voltage level of available power needs to be changed to meet the requirements of circuitry that operates at a higher or lower voltage than the available voltage.
Some voltage converters have an isolation barrier between the primary side that receives an input voltage to be translated and the secondary side. Isolation barrier refers to an electrical isolation between two domains. Such isolation may be needed because during normal operation a large DC or transient voltage difference exists between the domains. For example, one domain may be “grounded” at a voltage which is switching with respect to earth ground by hundreds or thousands of volts. Another reason for such isolation is based on safety, even when the expected voltage difference between the domains is small in normal operation. When a voltage converter starts up, it can take time until the secondary side receives sufficient power to also start up. Thus, the primary side may be operational before the secondary side. When operation of the voltage converter depends on feedback from the secondary side, the voltage converter still needs to operate as the secondary side begins to receive power under start-up conditions. Improvements in start-up operations of voltage converters are desirable.